Protein structure and dynamics were investigated in solution and in the crystalline state using nuclear magnetic resonance spectroscopy in order to understand function. Studies were carried out on (a) staphylococcal nuclease, calcium dependent phosphodiesterase and (b) III (Glc) the phosphate carrier protei component of the bacterial PTS system. A. S. nuclease. We have succeeded in assigning nearly all proton, carbo and nitrogen NMR signals of the S. nuclease/pdTp/Ca2+ ternary complex by combining isotopic enrichment with sophisticated two- and three-dimensional NMR techniques. These assignments together with NOE and relaxation measurements show that the enzyme backbone structure in solution is similar to that in the crystalline state except in the omega loop and at the active site, both of which are more flexible than in the crystalline state. The flexibility in these regions provide an attractive explanation of the diversity of substrates hydrolyzed by the enzyme. Current work is focused upon studies of the interaction of Ca with the enzyme and upon relating changes in sequence with changes in structure and function. B. III(Glc). We are determining the three dimensional solution structure of III(Glc) in order to provide a basis for understanding the phosphate transporting and regulatory functions of this protein. A variety of high-quality heteronuclear edited three-dimensional NMR spectra have been obtained and are currently being; analyzed to obtain signal assignments. These assignments together with heteronuclear 3D NOESY spectra will then be used to derive the protein structure. The significance of the project is the development of techniques that provide protein structures in solution that will permit one to obtain a rational basis for understanding function in terms of structure.